This invention relates to a relatively low cost sensor which is easily and securely mounted to a brake pad.
Brakes in modern vehicles typically include a replaceable brake pad with a friction material added to a metal backing plate. One main type of such brake pads is for use in a cam-type brake. In these type brakes, a brake table provides the backing plate and is generally curved along the circumference of a vehicle wheel. A friction material is formed on the top surface of the table and is selectively brought into contact with the wheel.
In another type of brake, a generally planar disc is selectively brought into contact with a rotating member. The discs have friction material formed on a backing plate.
In either type of brake, the friction material is typically riveted to the underlying metal backing plate. The friction material wears with use of the brake, and it is desirable to have a sensor for indicating when the friction material has worn. These sensors provide operator feedback of when the brake pads should be replaced. The sensors have used many diverse algoriths and techniques to identify wear.
In the past, monitoring the sensors have required relatively complex and expensive structures. Often the proposed sensors have necessarily changed the formation of the friction material or the backing plate. Further, the prior art sensors have often required expensive and unique electrical connectors.
As one example, the sensors have sometimes been threaded devices which require threading of the backing plate. This is expensive and undesirable. Some proposed sensors have been inserted through the lining in the brake, and thus require modification to the lining. Such sensors have often required a pigtail connector design, with the connector being attached by the brake pad manufacturer. Further, this type sensor has often required miniaturized connector designs. All of the above result in a brake that is undesirably expensive and less robust than would be desired.
In a disclosed embodiment of this invention, a sensor is attached to a hole in the backing plate, and most preferably, to one of the rivet holes in the backing plate. That is, one of the rivet holes which typically receives a rivet to secure the friction material to the plate is left without a rivet. The sensor is mounted in the rivet hole. The sensor preferably has an outer shoulder which abuts a rear; face of the backing plate, and a forwardly extending sensor portion extending through the hole in the backing plate. Preferably, the forwardly extending portion has an outer diameter that is smaller than the inner diameter of the hole.
The sensor is locked to the backing plate by a locking sleeve received on the sensor from the lining side of the backing plate. The locking sleeve has a shoulder portion which has an outer diameter greater than the inner diameter of the hole such that the locking sleeve abuts one side of the plate and captures the sensor. Preferably, the locking sleeve has a finger which snaps into a groove in the sensor securing the sensor to the sleeve. Most preferably, the finger and groove extend around the entire circumference of the sleeve and sensor portion.
The above-described sensor is relatively easy to assemble and is relatively inexpensive. These and other features of the present invention can be best understood from the following specification and drawings, the following which is a brief description.